U.S. patent number 7,751,765 [Application Number 11/438,738] was granted by the patent office on 2010-07-06 for image forming apparatus with transferring member to transfer toner image onto the recording medium.
This patent grant is currently assigned to Konica Minolta Business Technologies, Inc.. Invention is credited to Kazuteru Ishizuka, Shigetaka Kurosu, Satoshi Nishida.
United States Patent |
7,751,765 |
Kurosu , et al. |
July 6, 2010 |
Image forming apparatus with transferring member to transfer toner
image onto the recording medium
Abstract
There is described an image forming apparatus, which prevent
toner from contaminating inside of the apparatus and the recording
medium. The apparatus includes: an image bearing member; and a
transferring member that press-contacts the image bearing member
for transferring the toner image onto the recording medium. When
the transferring member transfers the toner image onto the
recording medium in such a state that the toner image is extended
from an edge of the recording medium, the following relationship is
fulfilled, 0<A<B where A: a length of an extended portion
that the toner image residing on the image bearing member is
extended from the edge of the recording medium; and B: a length of
a distance from the edge of the recording medium to a position at
which the transferring member and the image bearing member start to
contact each other.
Inventors: |
Kurosu; Shigetaka (Hino,
JP), Nishida; Satoshi (Saitama, JP),
Ishizuka; Kazuteru (Hachioji, JP) |
Assignee: |
Konica Minolta Business
Technologies, Inc. (JP)
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Family
ID: |
37694449 |
Appl.
No.: |
11/438,738 |
Filed: |
May 22, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070025780 A1 |
Feb 1, 2007 |
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Foreign Application Priority Data
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Aug 1, 2005 [JP] |
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2005-222665 |
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Current U.S.
Class: |
399/313; 399/324;
399/330; 399/384; 399/331; 399/341 |
Current CPC
Class: |
G03G
15/16 (20130101); G03G 2215/1614 (20130101) |
Current International
Class: |
G03G
15/20 (20060101) |
Field of
Search: |
;399/45,313,324,330-331,341,384 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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5-158361 |
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Jun 1993 |
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JP |
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6-118805 |
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Apr 1994 |
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JP |
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08095963 |
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Apr 1996 |
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JP |
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2004-309696 |
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Nov 2004 |
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JP |
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2005-017570 |
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Jan 2005 |
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JP |
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Other References
English translation of Nagai et al. (JP pub 08-095963), published
Apr. 12, 1996. cited by examiner .
English translation of Mori (JP pub 2004-309696), published Nov. 4,
2004. cited by examiner.
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Primary Examiner: Gray; David M
Assistant Examiner: Evans; Geoffrey T
Attorney, Agent or Firm: Cantor Colburn LLP
Claims
What is claimed is:
1. An image forming apparatus, comprising: an image bearing member
to bear a toner image; a recording medium that accepts the toner
image to be transferred from the image bearing member; and a
transferring member that press-contacts the image bearing member
while pressing the recording medium against the toner image
residing on the image bearing member so as to transfer the toner
image onto the recording medium; wherein, when the transferring
member transfers the toner image residing on the image bearing
member onto the recording medium in such a state that the toner
image is extended from an edge of the recording medium, a
positional relationship between the transferring member, the
recording medium and the image bearing member is established so as
to fulfill a specific relationship of: 0<A<B where A is
defined as a length of an extended portion of the toner image
residing on the image bearing member, the extended portion being
relatively extended from the edge of the recording medium; and B is
defined as a length of a distance from the edge of the recording
medium to an edge of a contacting area at which the transferring
member and the image bearing member press-connect each other
outside the edge of the recording medium; and wherein a direction
of the length A is substantially the same as that of the length
B.
2. The image forming apparatus of claim 1, further comprising: a
photoreceptor member to form a toner image thereon wherein the
photoreceptor member also serves as the image bearing member, and
the positional relationship between the transferring member, the
recording medium and the photoreceptor member is established so as
to fulfill the specific relationship of: 0<A<B.
3. The image forming apparatus of claim 1, further comprising: a
photoreceptor member to form a toner image thereon; wherein the
image bearing member is an intermediate transfer member, onto which
the toner image formed on the photoreceptor member is transferred,
and, from which the toner image, transferred from the photoreceptor
member, is further transferred onto the recording medium; and
wherein the positional relationship between the transferring
member, the recording medium and the intermediate transfer member
is established so as to fulfill the specific relationship of
0<A<B.
4. The image forming apparatus of claim 1, further comprising: a
conveying section to convey the recording medium to a transferring
position at which the image bearing member bearing the toner image
and the transferring member oppose to each other; wherein the
transferring member is a transferring roller, and when the
transferring roller transfers the toner image residing on the image
bearing member onto the recording medium in such a state that the
toner image is extended from an edge of the recording medium
located downstream in a conveyance direction of the recording
medium, the length B fulfills a relation shown as follows,
B=(r.sup.2-(r-d).sup.2).sup.1/2 where d is defined as a thickness
of the recording medium; r is defined as a radius of the
transferring roller.
5. The image forming apparatus of claim 1, wherein the transferring
member is provided with an elastic layer, a hardness of which is in
a range of 30.degree.-70.degree. in Asker C hardness.
6. The image forming apparatus of claim 1, further comprising: a
conveying section to convey the recording medium to a transferring
position at which the image bearing member bearing the toner image
and the transferring member oppose to each other; and a transfer
bias applying section to apply a transferring bias to the recording
medium; wherein, when the transferring roller transfers the toner
image residing on the image bearing member onto the recording
medium in such a state that the toner image is extended from an
edge of the recording medium located downstream in a conveyance
direction of the recording medium, a value of the transferring
bias, to be applied at a time when the extended portion of the
toner image passes through the transferring position, is smaller
than that of the transferring bias, to be applied at a time when a
center portion of the recording medium in a conveyance direction of
the recording medium passes through the transferring position.
7. The image forming apparatus of claim 1, wherein the image
forming apparatus is a color image forming apparatus, and, when the
transferring member transfers the toner image residing on the image
bearing member onto the recording medium in such a state that the
toner image is extended from the edge of the recording medium, at
least the extended portion of the toner image includes
substantially no black toner.
Description
This application is based on Japanese Patent Application NO.
2005-222665 filed on Aug. 1, 2005 in Japanese Patent Office, the
entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, such
as a copier, a printer, etc.
Conventionally, an image forming apparatus employing the
electro-photographic method, such as a copier, a printer, etc., is
provided with a photoreceptor member serving as a image bearing
member, a charging device, a scanning unit, a developing roller,
which are sequentially disposed around the photoreceptor member,
and a transferring roller serving as a transferring member.
In the image forming apparatus mentioned in the above, a surface of
the photoreceptor member is uniformly charged by the charging
device, and then, an electrostatic latent image is formed on the
charged surface of the photoreceptor member by scanning a laser
beam modulated on the basis of the image data and emitted from the
scanning unit onto it. Then, the developing roller develops
electrostatic latent image with toner to form a toner-image on the
surface of the photoreceptor member. Successively, the toner image
formed on the surface of the photoreceptor member is transferred
onto a paper sheet serving as a recording medium by employing the
transferring roller. Through the abovementioned process, the image
can be formed on the paper sheet.
Further, there has been well known a color image forming apparatus,
or the like, which is provided with a plurality of developing
rollers each of which corresponds to each of unicolor images
(primary colors) and an intermediate transfer member, serving as
another image bearing member, for overlapping the unicolor images
respectively formed on the photoreceptor member with each other on
it, so as to form a full color toner image by sequentially
overlapping the unicolor images one by one with each other. Then,
the color image forming apparatus forms a full color image on the
paper sheet by transferring the full color toner image on to the
paper sheet by employing the transferring roller serving as a
transferring member.
Conventionally, such the image forming apparatus mentioned in the
above has formed the image on the paper sheet with margin spaces
located around a peripheral area of the paper sheet. However,
recently, there has been getting proliferated in the market such a
print-outputting method, called as a marginless print, that extends
the image forming area up to at least one of the margin spaces.
For instance, there has been well known a document processing
technology, called as an index print, for automatically adding
index characters to the left edge portion (or the right edge
portion). Further, in recent years, there has been getting also
proliferated in the market such a printing method, called as a
whole marginless print, that extends the image forming area up to
at all of the margin spaces without having any margin space, when
printing a pattern image, a photographic image, etc.
Incidentally, when a positional deviation, caused by the erroneous
conveyance timing shift, etc., is generated between the toner image
formed on the image bearing member and the paper sheet, the
position of the image formed on the paper sheet is different from
that of the original image read from the document. In almost cases,
amounts of the erroneous conveyance timing shift are not constant,
but differ from each other depending on the differences between
sizes and kinds of the paper sheets or kinds of containers
accommodating the paper sheets.
Accordingly, when conducting the marginless print, a positional
deviation generated between the toner image and the paper sheet
causes a defect of the image transferred onto the paper sheet,
resulting in a formation of a very awkward image. In addition, the
defect of the image is also caused by the size variation of the
paper sheets.
To overcome the abovementioned drawbacks, considering the
positional deviation caused by the erroneous conveyance timing
shift and the size variation of the paper sheets, there has been
conducted such an operation that a large-sized toner image, having
a sufficient allowance, is formed on the image bearing member, so
as to form a good image over the paper sheet without forming any
defect, even if the erroneous conveyance timing shift of the paper
sheet occurs.
When the marginless print is conducted over the edge portion of the
paper sheet by employing the abovementioned operation, there has
raised a problem that the surface of the transferring roller is
contaminated by toner, and such the contaminated transferring
roller causes the toner scattering inside the printer apparatus.
Specifically, when the toner image, residing on the image bearing
member and extended from the recording medium, directly contact the
transferring roller, the toner is firmly absorbed and attached onto
the transferring roller due to a combination of the contacting
pressure of the transferring roller and the transferring electric
field. It is quite difficult to clean the toner firmly absorbed and
attached onto the transferring roller, and, especially for the high
density image, even if the mechanical cleaning device, such as
blade, etc., is employed for cleaning, sometimes, the reverse
surface of the paper sheet would be contaminated, due to an
occurrence of the toner passing-through phenomenon.
Further, when the polymerized toner, whose particle diameter is
minimized and whose circularity is high, are employed in order to
cope with the recent demands for high quality imaging, or when an
amount of attached toner is relatively high as in the full-color
image forming apparatus, it has tended to become more difficult
than ever to secure the cleaning efficiency.
Still further, when the residual toner, which are not transferred
onto the paper sheet, increase more than ever, there has raised a
big problem that the toner scattering phenomenon causes the
contamination inside the apparatus.
To solve the abovementioned problems, the several countermeasures
have been proposed in this field.
For instance, to solve the problem of the contamination on the
transferring roller when the index print operation is conducted at
the edge portion of the paper sheet, Patent Document 1 sets forth a
solution in which an interval between paper sheets is set at a
value wider than that of a normal case, and the transferring
process and the cleaning sequence are alternately conducted.
Further, Patent Document 2 sets forth a measure for preventing the
contamination of the transferring roller and the contamination of
the reverse surface of the paper sheet by conducting the
transferring operation with a gap between the photoreceptor member
and the transferring roller.
Still further, Patent Document 3 sets forth a method for making it
possible to prevent an occurrence of the contamination so as to
form a good full image by conducting the image forming operation in
a state that a guiding paper sheet, which is larger than the paper
sheet, is extended from the four edges of the paper sheet.
Yet further, Patent Document 4 sets forth a measure for cleaning
the transferring roller by employing the cleaning blade.
[Patent Document 1] Tokkai 2004-309696 (Japanese Non-Examined
Patent Publication)
[Patent Document 2] Tokkaihei 5-158361 (Japanese Non-Examined
Patent Publication)
[Patent Document 3] Tokkai 2005-17570 (Japanese Non-Examined Patent
Publication)
[Patent Document 4] Tokkaihei 6-118805 (Japanese Non-Examined
Patent Publication)
However, the conventional technologies mentioned in the above still
include various kinds of drawbacks to be solved.
According to the technology set forth in Patent Document 1, when
forming a high density image so as to output it onto the recording
medium, repetitions of plural cleaning operations should be
necessary for achieving the sufficient cleaning effect, resulting
in an extreme deterioration of the print productivity.
According to the technology set forth in Patent Document 2, it is
impossible to sufficiently cope with the thickness changes between
the recording mediums. Further, since a discharging phenomenon is
liable to occur due to the loose contacting state between the
photoreceptor member and the transferring roller, sometimes, it is
impossible to obtain a good image. In addition, since the
conveyance efficiency of the recording medium is lowered, the
problem, such as the misalignment of transferred images, etc., is
liable to occur.
According to the technology set forth in Patent Document 3, there
have been arisen not only the problem of wasting the guide papers,
but also various kinds of other problems in regard to the
contacting property between the paper sheet and the guide paper.
When those are close-contacted with each other by the electrostatic
action, those would possibly shift or separate form each other in a
mid course of the conveying operation.
According to the technology set forth in Patent Document 4, the
cleaning mechanism has become complicated, and further, sometimes,
a toner filming phenomenon has occurred on the transferring roller.
Further, when the toner, such as the polymerized toner, etc., whose
circularity is high, are employed, sometimes, a problem with
respect to the cleaning efficiency has been arisen.
SUMMARY OF THE INVENTION
To overcome the abovementioned drawbacks in conventional
image-recording apparatus, it is an object of the present invention
to provide an image forming apparatus, in which a toner
contamination on the transferring roller, which further causes
another toner contamination on the reverse surface of the recording
medium, and toner contaminations due to the toner scattering
actions in the apparatus are prevented.
Accordingly, to overcome the cited shortcomings, the abovementioned
object of the present invention can be attained by an image forming
apparatus described as follow. (1) An image forming apparatus,
comprising: an image bearing member to bear a toner image; a
recording medium that accepts the toner image to be transferred
from the image bearing member; and a transferring member that
press-contacts the image bearing member for transferring the toner
image onto the recording medium; wherein, when the transferring
member transfers the toner image residing on the image bearing
member onto the recording medium in such a state that the toner
image is extended from an edge of the recording medium, a following
relationship is fulfilled, 0<A<B
where A: a length of an extended portion that the toner image
residing on the image bearing member is extended from the edge of
the recording medium; B: a length of a distance from the edge of
the recording medium to a position at which the transferring member
and the image bearing member start to contact each other outside
the edge of the recording medium; and wherein directions that
regulate A and B are the same as each other.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments will now be described, by way of example only, with
reference to the accompanying drawings which are meant to be
exemplary, not limiting, and wherein like elements are numbered
alike in several Figures, in which:
FIG. 1 shows an overall configuration of a color image forming
apparatus, serving as an example of an image forming apparatus
embodied in the present invention;
FIG. 2 shows a block diagram of a controlling system for conducting
controlling operations in a marginless print mode of the image
forming apparatus shown in FIG. 1;
FIG. 3 shows an image forming area on a photoreceptor drum in a
marginless print mode of the image forming apparatus shown in FIG.
1;
FIG. 4 shows a cross sectional view of a secondary transferring
roller and a recording medium in a main-scanning direction,
indicating a state of secondary transferring operation in a
marginless print mode of the image forming apparatus shown in FIG.
1;
FIG. 5(a) and FIG. 5(b) show cross sectional views of a secondary
transferring roller and a recording medium in a sub-scanning
direction, FIG. 5(a) indicating a state at the time of commencing a
transferring operation, and FIG. 5(b) indicating a state at the
time of completing the transferring operation;
FIG. 6 shows an enlarged cross sectional view of FIG. 5(b);
FIG. 7 shows a waveform and a time chart of a transferring bias (a
current value) for a secondary transferring operation; and
FIG. 8(a) and FIG. 8(b) show schematic diagrams indicating
relationship between an image forming area and a recording medium
area at the time of a secondary transferring operation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, an image forming apparatus embodied in the
present invention will be detailed in the following.
The image forming apparatus shown in FIG. 1 is a color image
forming apparatus provided with four sets of image forming
sections. Concretely speaking, the color image forming apparatus is
provided with image forming sections 10Y, 10M, 10C, 10K, an
intermediate transfer unit 7 having an endless belt-type
intermediate transfer member, a paper conveyance and fixing section
24, a controlling section 30 for totally controlling the operations
of the apparatus as a whole, an operation inputting section 104, a
displaying section 17, etc. Further, an original document reading
device SC is disposed at the upper side of a main body AA of the
color image forming apparatus.
The image forming section 10Y for forming a toner image of color Y
(Yellow) includes a photoreceptor drum 1Y serving as an image
forming element, and further includes a charging device 2Y, an
exposing device 3Y, a developing device 4Y, a primary transferring
roller 5Y serving as a primary transferring device and a cleaning
device 6Y, all of which are disposed at respective positions in the
peripheral space around the circumferential surface of the
photoreceptor drum 1Y. Further, the image forming section 10M for
forming a toner image of color M (Magenta) includes a photoreceptor
drum 1M serving as an image forming element, and further includes a
charging device 2M, an exposing device 3M, a developing device 4M,
a primary transferring roller 5M serving as a primary transferring
device and a cleaning device 6M, all of which are disposed at
respective positions in the peripheral space around the
circumferential surface of the photoreceptor drum 1M. Still
further, the image forming section 10C for forming a toner image of
color C (Cyan) includes a photoreceptor drum 1C serving as an image
forming element, and further includes a charging device 2C, an
exposing device 3C, a developing device 4C, a primary transferring
roller 5C serving as a primary transferring device and a cleaning
device 6C, all of which are disposed at respective positions in the
peripheral space around the circumferential surface of the
photoreceptor drum 1C. Yet further, the image forming section 10K
for forming a toner image of color K (Black) includes a
photoreceptor drum 1K serving as an image forming element, and
further includes a charging device 2K, an exposing device 3K, a
developing device 4K, a primary transferring roller 5K serving as a
primary transferring device and a cleaning device 6K, all of which
are disposed at respective positions in the peripheral space around
the circumferential surface of the photoreceptor drum 1Y.
An OPC photoreceptor member, an aSi (amorphous Silicon)
photoreceptor member, etc., which are made of organic semiconductor
material, are preferably employed for the photoreceptor drums 1Y,
1M, 1C, 1K. A scotron charging device having a control grid is
preferably employed for the charging devices 2Y, 2M, 2C, 2K. A
scanning exposure device having a laser light source or a scanning
exposure device having a LED (Light Emitting Diode) light source,
etc., is preferably employed as each of the exposing devices 3Y,
3M, 3C, 3K. In the embodiment shown in FIG. 5, each of the exposing
devices 3Y, 3M, 3C, 3K has a laser light source.
Either one component developer or two components developer can be
employed in the developing devices 4Y, 4M, 4C, 4K. The reversal
developing method, for attaching toner, charged at a polarity same
as that of an electrostatic latent image, to the exposed area of
the circumferential surface of the photoreceptor drum, is
preferably employed for the developing device. As will be described
later, each of the developing devices 4Y, 4M, 4C, 4K conducts a
developing operation while applying a developing bias voltage in
which DC bias voltage and AC bias voltage are overlapped with each
other.
A transferring device having either a transferring roller or a
corona discharger is employed as each of the primary transferring
devices 5Y, 5M, 5C, 5K. The transferring device, having the
transferring roller, also has a transferring power source for
applying the transferring current to the transferring roller.
The intermediate transfer unit 7 includes a plurality of rollers
71-76 and an intermediate transfer member 70 shaped in an endless
semiconductor belt, which is threaded on the plurality of rollers
71-76 so as to circulate around them (an example of the image
bearing member).
In image forming section 10Y, according with the anti-clockwise
rotating action of the photoreceptor drum 1Y as indicated by the
arrow shown in FIG. 1, the toner image of color Y is formed on the
photoreceptor drum 1Y through the process including the charging
operation conducted by the charging device 2Y, the exposing
operation conducted by the exposing device 3Y and the developing
operation conducted by the developing device 4Y. Further, the toner
image formed on the photoreceptor drum 1Y is transferred onto the
intermediate transfer member 70 by activating the primary
transferring roller 5Y.
Through the process same as that performed in image forming section
10Y, the toner images of color M, color C and color K, are also
formed on the photoreceptor drums 1M, 1C, 1K in the image forming
sections 10M, 10C, 10K, respectively, and then, are sequentially
transferred onto the intermediate transfer member 70 in such a
manner that the toner images of color Y, color M, color C and color
K overlap with each other. As a result, a full color toner image is
formed on the intermediate transfer member 70. Then, the full color
toner image formed on the intermediate transfer member 70 is
transferred onto a recording medium P by pressing a secondary
transferring roller 5A against the recording medium P so that the
recording medium P press-contacts the full color toner image.
Successively, the full color toner image is fixed onto the
recording medium P in the paper conveyance and fixing section 24,
and then, the recording medium P having the fixed toner image is
ejected to an outside of the apparatus by activating an ejecting
roller 28.
It is applicable that the rotating action of the secondary
transferring roller 5A is driven by the circulating action of the
intermediate transfer member 70 or the roller 74, or independently
driven in a direction same as the circulating direction of the
intermediate transfer member 70 at the contacting point.
As shown in FIG. 4, the secondary transferring roller 5A employed
in the present embodiment is so constituted that an elastic layer
302 is formed on the whole circumferential surface of a core metal
301 shaped in a cylindrical form.
Various kinds of materials, such as an EPDM, an urethane, a NBR, a
silicon rubber, a rubber material in which conductive materials,
such as carbon black, a metal oxide, etc., are mingled with the IR,
etc. for adjusting its resistivity, a foam material made of one of
the abovementioned materials, etc., can be cited as an elastic
material to be employed for the elastic layer 302. The secondary
transferring roller 5A is mounted in such a manner that the
secondary transferring roller 5A press-contacts the recording
medium P with a predetermined pressure so as to oppose against the
elasticity of the elastic layer at the time of the secondary
transferring operation. In the present embodiment, a transferring
nip section having a width of several millimeters is formed on the
secondary transferring roller 5A.
Further, at the time of the secondary transferring operation, the
transferring bias is applied to the secondary transferring roller
5A from a transferring bias applying section 200 (shown in FIG. 2).
In the present embodiment, the transferring current is applied as
the transferring bias.
Each length of the intermediate transfer member 70 and secondary
transferring roller 5A in a direction substantially orthogonal to
the conveyance direction of the recording medium P (namely, a width
direction of the recording medium P) is set at such a value that
each length is longer than that of a recording medium having a
maximum size allowable (usable) for the image forming
apparatus.
A heat roller fixing unit having a heating roller 24a and a
pressing roller 24b is employed as the paper conveyance and fixing
section 24.
In the duplex image forming operation, the recording medium P, on
the obverse surface of which the image is already formed and fixed,
is guided and conveyed into a conveyance path 100 by a guiding
member 204 after passing through a fixing eject roller 27. Then,
after the switch backing operation performed in a switch backing
path 101, the recording medium P is again introduced into the
secondary transferring roller 5A from a paper re-feeding path 102
through a conveyance roller 103 so as to conduct a reverse image
forming operation by transferring a toner image onto the reverse
surface of the recording medium P by activating the secondary
transferring roller 5A.
Through the same process as aforementioned, the color toner image
to be formed on the reverse surface of the recording medium P is
formed on the intermediate transfer member 70, and then,
transferred onto the reverse surface of the recording medium P from
the intermediate transfer member 70.
The recording medium P, which is accommodated in any one of paper
feeding trays 20A, 20B, 20C, is conveyed out by any one of paper
feeding sections 21A, 21B, 21C, and then, conveyed to a
registration roller 23 by an intermediate conveyance roller 22. The
registration roller 23, which is an example of a conveyance section
for conveying the recording medium to the transferring position at
which the intermediate transfer member bearing the toner image is
opposed against the secondary transferring roller, is activated so
as to be synchronized with the actions of the image forming
sections 10Y, 10M, 10C, 10K and the intermediate transfer member
70, in order to feed the recording medium P to the transferring
position at which the intermediate transfer member 70 bearing the
toner image is opposed against the secondary transferring roller
5A. The recording mediums whose sizes are different from each other
are respectively accommodated in the paper feeding trays 20A, 20B,
20C. Based on the command signal inputted from the operation
inputting section 104, the recording medium having a specific size
is fed from corresponding one of the paper feeding trays 20A, 20B,
20C.
After the toner image transferring operation is completed, the
intermediate transfer member 70 is cleaned by a cleaning device
6A.
Further, the color image forming apparatus is provided with a
selector switch (not shown in the drawings) for switching a
printing mode to the marginless print mode in which the image
forming area is extended up to at least one of the margin spaces
located at the peripheral edge area of the recording medium. The
color image forming apparatus is so constituted that the marginless
print is conducted when the marginless print mode is selected by
switching the selector switch.
FIG. 2 shows a block diagram of a controlling system for conducting
such the marginless print mode. The configurations of the exposing
devices 3Y, 3M, 3C, 3K are common to each other and the
configurations of the developing devices 4Y, 3M, 3C, 3K are also
common to each other, and are respectively indicated by numerals 3,
4 in FIG. 2.
As shown in FIG. 2, the controlling section 30 is constituted by an
I/F (Interface) section 31, a ROM (Read Only Memory) 32, a RAM
(Random Access Memory) 33, a CPU (Central Processing Unit) 34,
etc., in order to control various kinds of devices coupled to the
I/F section 31, based on the controlling programs and the
controlling data stored in the ROM 32.
The displaying section 17 for displaying errors and a status of
each of the sections, etc., the exposing device 3, the developing
device 4, the secondary transferring roller 5A, a transfer bias
applying section 200, the operation inputting section 104 for
inputting the marginless print mode and setting the size of the
recording medium P, etc., are electrically coupled to the I/F
section 31.
The data of the image forming area on the photoreceptor drum in the
marginless print mode, transferring current values to be applied to
the secondary transferring roller 5A, etc., are stored in the ROM
32.
A plurality of data sets can be stored in the RAM 33, only during
the time when the electric power is fed to the RAM 33. A storage
area in which various kinds of data, such as image data for
conducting the image forming operation for forming the image on the
recording medium P, etc., a working area to be used by the CPU 34,
etc., are provided in the RAM 33.
The CPU 34 develops a program designated from the various kinds of
programs stored in the ROM 32 into the working area provided in the
RAM 33, so as to conduct various kinds of operations based on the
program in response to the inputted signals sent from each
inputting section.
Incidentally, the image forming area on the photoreceptor drum
includes a first area that extends in a main-scanning direction and
a second area that extends in a sub-scanning direction. After the
exposing device conducts the exposing operation based on the image
data corresponding to either the first area or the second area so
as to form the electrostatic latent image, the toner image is
formed by developing the electrostatic latent image. The
main-scanning direction is substantially the same as the axial
direction of the photoreceptor drum 1, and also, substantially the
same as the width direction of the recording medium. Further, in
the secondary transferring operation, the main-scanning direction
is substantially the same as the axial direction of the secondary
transferring roller. While, the sub-scanning direction is
substantially the same as the rotating direction of the
photoreceptor drum 1, and, in the secondary transferring operation,
substantially the same as the conveyance direction of the recording
medium. In the marginless print mode, this image forming area
differs from that in the normal print mode with edge margins. In
addition, this image forming area also varies depending on the size
of the recording medium.
Referring to the case in which the marginless print operation is
applied to all of four edge portions located at peripheral edge
area of the recording medium, the image forming area and the
secondary transferring operation will be detailed in the
following.
In response to the instruction for commencing the image forming
operation after the marginless print mode and the size of the
recording medium are set, the controlling section 30 reads out the
data of the image forming area from the ROM 32, and then, activates
the exposing device 3 so as to form the electrostatic latent image
on the photoreceptor drum 1 within such the image forming area that
is extended from the four edge portions of the recording medium P,
based on the readout data.
Accordingly, when the controlling section 30 conducts the
marginless print mode, the exposing device 3 forms the
electrostatic latent image extending over the four edge portions of
the recording medium P. Successively, the developing device 4
develops the electrostatic latent image, and then, the full color
toner image, formed by overlapping the electrostatic latent images
with each other on the intermediate transfer member 70, is
secondary transferred onto the recording medium P, conveyed to the
transferring position, in such a manner that the full color toner
image extends out from the four edge portions of the recording
medium P. As a result, the marginless print having no margin spaces
at the edge portions located at the peripheral edge area of the
recording medium P can be achieved. Further, at the time of the
secondary transferring operation, the controlling section 30
controls the transferring bias applying section 200 so as to apply
the transferring bias current to the secondary transferring roller
5A.
FIG. 3 shows the image forming area on the photoreceptor drum 1 in
the marginless print mode. In FIG. 3, the circumferential surface
of the photoreceptor drum 1 is depicted as a plane surface.
Further, in FIG. 3, alternate long and two short dashes lines
indicate the photoreceptor drum 1, solid lines indicate the four
edges of the image forming area, alternate long and short dash
lines indicate the four edges of the recording medium P (or the
position of the recording medium P) at the time of the secondary
transferring operation, and broken lines indicate the outside area
from four edges of the recording medium P, where the secondary
transferring roller 5A press-contacts the intermediate transfer
member 70.
FIG. 4 shows a cross sectional view of the secondary transferring
roller 5A and the recording medium P in the main-scanning
direction, indicating a state of secondary transferring operation
after the toner image, formed within the image forming area on the
photoreceptor drum as shown in FIG. 3, is primarily transferred
onto the intermediate transfer member.
Further, FIG. 5(a) and FIG. 5(b) show cross sectional views of the
secondary transferring roller 5A and the recording medium P in the
sub-scanning direction. FIG. 5(a) indicates a state at the time of
commencing the transferring operation, while FIG. 5(b) indicates a
state at the time of completing the transferring operation.
Further, during the transferring operation, the secondary
transferring roller 5A rotates in a direction indicated by the
arrow shown in FIG. 5(a) and FIG. 5(b).
Still further, FIG. 6 shows an enlarged cross sectional view of
FIG. 5(b).
Incidentally, in FIGS. 4 through 6, the roller 74, shown in FIG. 1,
is omitted.
As indicated in the above, when conducting the marginless print for
forming an image all over the four edges of the recording medium P,
the positions of four edges of the image forming area are set at
such positions that are located outside the four edges of the
recording medium P and do not exceed four positions at each of
which the secondary transferring roller 5A and the intermediate
transfer member 70 contact each other outside each of the four
edges of the recording medium P.
& Concretely speaking, the image forming area is established so
as to fulfill the relationships shown as follow. 0<A1<B1
0<A2<B2
where, A1: length of a portion of the image forming area, which is
extended from the edge of the recording medium P in the
sub-scanning direction, B1: length of a distance from an edge of
the recording medium P to a position at which the secondary
transferring roller 5A and the intermediate transfer member 70
start to contact each other outside the edge of the recording
medium P in the sub-scanning direction, A2: length of a portion of
the image forming area, which is extended from the edge of the
recording medium P in the main-scanning direction, B2: length of a
distance from an edge of the recording medium P to a position at
which the secondary transferring roller 5A and the intermediate
transfer member 70 start to contact each other outside the edge of
the recording medium P in the main-scanning direction.
By setting the image forming area so as to fulfill the above
relationships, it becomes possible to fulfill the relationship
shown as follow. 0<A<B
where, A (mm): length of a portion of the toner image borne by the
intermediate transfer member 70, which is extended from an edge of
the recording medium P, when the toner image borne by the
intermediate transfer member 70 is transferred onto the recording
medium P in a state that the toner image is extended from the edge
of the recording medium P, B (mm): length of a distance from an
edge of the recording medium P to a position at which the secondary
transferring roller 5A and the intermediate transfer member 70
start to contact each other outside the edge of the recording
medium P, and
wherein directions that regulate A and B are the same as each
other, and in the present embodiment, equivalent to either the
main-scanning direction or the sub-scanning direction. According to
the above, the following features and effects can be achieved.
In the case of employing the secondary transferring roller of the
contacting method for the secondary transferring operation, when
the secondary transferring roller press-contacts the intermediate
transfer member while putting the recording medium P between them,
the recording medium P is cohered to the intermediate transfer
member due to an elastic deformation of the elastic layer of the
secondary transferring roller, while creating a space around the
recording medium P at this time. If the toner image is formed
within this space area, the secondary transferring roller is hardly
contaminated, since the secondary transferring roller does not
directly press-contact the toner image (compared to the contacting
state, an amount of toner flying in the space and adhering to the
secondary transferring roller is overwhelmingly small). Further,
even if the toner adheres onto the secondary transferring roller,
since its amount is very small and no pressure is applied to the
adhered toner, it becomes possible to easily clean the toner having
a little adhesive force. Accordingly, it becomes possible to
prevent the recording medium P from contaminating its reverse
surface due to the toner contamination of the secondary
transferring roller. In addition, it becomes possible for the
cleaning device, if provided, to easily clean the secondary
transferring roller, due to a little amount of residual toner to be
cleaned, resulting in a prevention of the toner scattering
contamination in the apparatus.
The bias cleaning operation can be preferably employed as a
cleaning method. An example of the bias cleaning operation is set
forth in Tokkai 2004-309696 (Japanese Non-Examined Patent
Publication). According to this method, to clean the residual toner
remained on the secondary transferring roller, the voltage having a
polarity same as that of the residual toner is applied to the
secondary transferring roller so as to transfer the residual toner
onto the image bearing member (in the present embodiment, the
intermediate transfer member), and then, the residual toner are
removed by the cleaning device for the image bearing member (in the
present embodiment, the intermediate transfer member).
Further, in the present embodiment, by setting the image forming
area, it is possible to achieve the abovementioned effect without
complicating the configuration.
As mentioned in the foregoing, it is possible to always keep the
secondary transferring roller 5A in a clean state, and therefore,
it becomes possible to achieve an image forming operation in which
a good image quality is continuously maintained.
Next, the method for finding B1 and B2 will be detailed in the
following.
Initially, B1 is found according to the equation shown as follow.
B1=(r.sup.2-(r-d).sup.2).sup.1/2
where, d: thickness of the recording medium P as shown in FIG. 6,
r: radius of the secondary transferring roller.
Although FIG. 6 is an enlarged cross sectional view of FIG. 5(b)
indicating a state at the time of completing the transferring
operation, B1 is found according to the above equation as well even
in regard to FIG. 5(a) indicating a state at the time of commencing
the transferring operation.
Accordingly, A1 is established so as to fulfill the relationship
shown as follow. 0<A1<(r.sup.2-(r-d).sup.2).sup.1/2
Incidentally, the above relationship is established when assuming
that the secondary transferring roller is a rigid body. However,
even in the case that the elastic layer of the secondary
transferring roller elastically deforms as described in the present
embodiment, by setting A1 so as to fulfill the relationship
indicated in the above, the effect of preventing the contamination
can be attained. Further, when the secondary transferring roller
has the elastic layer, although the value of B1 depends on the
thickness "d" of the recording medium, a hardness of the elastic
layer of the secondary transferring roller, etc., the value of B1
can be found in advance by conducting an experiment and a
simulation.
Further, although the value of B2 depends on the thickness "d" of
the recording medium, a hardness of the elastic layer of the
secondary transferring roller 5A, etc., the value of B2 can be also
found in advance by conducting an experiment and a simulation.
In regard to the thickness "d" of the recording medium, it is
preferable that the values of B1 and B2 are determined in
conformity with the thickness of the thinnest recording medium
among the recording mediums to be possibly used in the image
forming apparatus concerned. Further, it is also preferable that
the image forming apparatus is provided with a device for detecting
the thickness of the recording medium, or is so constituted that
the thickness of the recording medium is inputted and set from the
operation inputting section 104, so as to display a warning message
on the displaying section 17 or ban the image forming operation,
when the thickness of the recording medium is further thinner than
that of the thinnest recording medium among the recording mediums
to be possibly used in the image forming apparatus concerned.
Incidentally, in the abovementioned embodiment, it is preferable
that the hardness of the elastic layer of the secondary
transferring roller 5A is in a range of 30.degree.-70.degree. in
Asker C hardness. By setting the hardness at a value equal to or
greater than 30.degree. of Asker C hardness, it becomes possible to
increase the values of B1 and B2, resulting in an improvement of
the contamination preventing effect for the secondary transferring
roller 5A. While, by setting the hardness at a value equal to or
smaller than 70.degree. of Asker C hardness, it becomes possible to
stably secure the transferring nip portion, and to improve the
micro contacting property for the surface of the recording medium
P, resulting in an improvement of the transferring stability.
Further, in the embodiment mentioned in the above, when the portion
of the image forming area, which is extended from an end of the
recording medium in the downstream side of the conveyance direction
of the recording medium (namely, the portion of A1) passes through
the transferring position (for instance, the transferring nip
portion), it is preferable that the value of transferring current
to be applied to the secondary transferring roller 5A is set at a
value smaller than that to be applied to the secondary transferring
roller 5A when the central portion of the recording medium in the
conveyance direction passes through the transferring position (for
instance, the transferring nip portion). By applying the
abovementioned operation, it becomes possible to decrease the value
of the transferring current when the toner residing on the portion,
extended from an end of the recording medium in the downstream side
of the conveyance direction of the recording medium, is secondary
transferred, and to prevent the toner from moving to the
transferring member more effectively, resulting in an improvement
of the effect for preventing the contamination. Incidentally,
hereinafter, the term of "when the portion of A1, or the central
portion of the recording medium in the conveyance direction passes
through the transferring position (for instance, the transferring
nip portion)" is defined as the time period while the portion of
A1, or the central portion of the recording medium in the
conveyance direction resides at the transferring position (for
instance, the transferring nip portion).
FIG. 7 shows a waveform and a time chart of the transferring bias
(the current value) for the secondary transferring operation. In
FIG. 7, the horizontal axis indicates a progress of time "t" from
the time when the central portion of the recording medium in the
conveyance direction arrives at an entrance position of the
transferring nip portion. The straight lines located at upper side
of the drawing indicate the recording medium and the toner image
residing on the intermediate transfer member, and also indicate the
transient status in which each portion of the recording medium and
the toner image is arriving at the entrance position of the
transferring nip portion according to the progress of time "t". For
instance, at time "t"=t2, the status in which the trailing edge of
the recording medium in the conveyance direction is positioned at
the entrance position of the transferring nip portion, namely, the
status in which the leading edge of the toner image residing on the
extended potion at the trailing edge side is positioned at the
entrance position of the transferring nip portion, is indicated.
The vertical axis indicates the transferring bias (the current
value). As the waveform shown in FIG. 7, it is preferable that,
considering the response time (normally, in a range of several
tens-100 msec) of the high voltage power source serving as a
transfer bias applying device, the transferring bias is switched at
time t1 before time t2, and, when the toner image extended from the
trailing edge of the recording medium (namely, the portion of A1)
passes through the transferring nip portion, the transferring bias
is reduced to substantially zero.
Incidentally, in the embodiment mentioned in the above, when
outputting the color image in the marginless print mode, by
substituting unicolor image data of yellow, magenta and cyan for
the black color image data corresponding to at least the extended
portion, namely, by substituting unicolor toner of yellow, magenta
and cyan for black color toner without employing the black color
toner at the time of image-forming operation, when the toner image
borne by the intermediate transfer member is transferred onto the
recording medium in the transferring operation, it is possible to
make the toner image residing on at least the extended portion
include substantially no black color toner. This makes it possible
to make the contamination of the reverse surface of the recording
medium, caused by the contamination of the transferring member,
unnoticeable. Incidentally, the term of "include substantially no
black color toner" means that the toner image includes no black
color toner developed as the image. Accordingly, the case in which
black color toner floating in the air, caused by scattering
actions, etc., are mingled into the toner image is included in the
scope of the term of "include substantially no black color
toner".
FIG. 8(a) and FIG. 8(b) show schematic diagrams indicating
relationship between the image forming area and the recording
medium area at the time of the secondary transferring operation,
when each of unicolor images of yellow, magenta, cyan and black is
formed all over the image forming area. In FIG. 8(a) and FIG. 8(b),
the solid lines, the alternate long and short dash lines, the
broken lines and the alternate long and two short dashes lines
indicate four edges of the image forming area, four edges of the
recording medium P (position of the recording medium P), a position
(four edges) at which the secondary transferring roller 5A and the
intermediate transfer member 70 contact each other outside the four
edges of the recording medium P and the image forming area of each
unicolor image of yellow, magenta, cyan and black,
respectively.
As shown in FIG. 8(a), it is applicable that the black toner image
is formed within an area equivalent to or narrower than that of the
recording medium P (namely, same as or inside the area of the
recording medium P. Further, in the case of the full color image
forming operation, the toner images of yellow, magenta and cyan are
also formed within the area), and, with respect to outside of the
abovementioned area, the black toner image is substituted by the
unicolor toner images of yellow, magenta and cyan without employing
the black toner so as to include substantially no black color
toner.
Incidentally, in the embodiment described in the foregoing,
although the secondary transferring roller 5A serves as a
transferring member embodied in the present invention, it is also
applicable that a blade or a belt is employed as a transferring
member, instead of the roller.
Further, in the embodiment described in the foregoing, the image is
formed in the marginless print mode, in such a manner that the
image covers all over the peripheral edge portion of the recording
medium P, namely, the four edge portions around the recording
medium P without including any margin space. However, it is
applicable that the marginless print mode is applied to, for
instance, a part of the peripheral edge portion of the recording
medium P. Concretely speaking, for instance, the marginless print
mode can be applied to only one side of the recording medium P in
the main-scanning direction (width direction), only both sides of
the recording medium P in the main-scanning direction, only one
side of the recording medium P in the sub-scanning direction
(conveyance direction) or only both sides of the recording medium P
in the sub-scanning direction.
Still further, when the marginless print mode is applied to a part
of the four edge portions of the recording medium P, it is
preferable that the marginless print mode is applied to three edge
portions of the recording medium P, excluding the leading edge
portion of the recording medium P in the conveyance direction. This
is because, when the marginless print mode is applied to the
leading edge portion of the recording medium P, there has been
liable to occur such a trouble that the recording medium P is wound
by the fixing roller. Accordingly, to avoid such the trouble, the
above measure is preferable.
Still further, in the embodiment described in the foregoing, the
color image forming apparatus employing the intermediate transfer
method is exemplified for explaining the image forming apparatus
embodied in the present invention. However, the scope of the image
forming apparatus embodied in the present invention is not limited
to the above. It is needless to say that a color image forming
apparatus employing the tandem image forming method instead of the
intermediate transfer member, or further, a monochrome image
forming apparatus is also applicable in the present invention.
Still further, in the color image forming apparatus employing the
tandem image forming method instead of the intermediate transfer
member or the monochrome image forming apparatus, the photoreceptor
member serving as an image bearing member and the transferring
member are disposed at positions opposed to each other, and the
toner image is transferred onto the recording medium P from the
photoreceptor member while the recording medium P is passing
through the nip potion formed between the photoreceptor member and
the transferring member.
Still further, in the embodiment described in the foregoing,
although the recording medium P is typically a paper sheet, such as
a normal paper or the like, the scope of the recording medium P is
not limited to the above. It is needless to say that a PET base
sheet for OHP use, etc. are also included in the scope of the
recording medium P.
Yet further, in the embodiment described in the foregoing, the
image forming apparatus employing the electro-photographic method
is exemplified as the image forming apparatus embodied in the
present invention. However, the scope of the image forming
apparatus embodied in the present invention is not limited to the
above. For instance, the present invention can be applied to such
an image forming apparatus that forms a toner image on the image
bearing member by emitting toner from a nozzle of a recording head,
and then, transfers the toner image onto the recording medium
P.
Referring to the examples, the present invention will be detailed
in the following. However, the scope of the present invention is
not limited to the examples detailed in the following.
Example 1
Employing the color image forming apparatus shown in FIG. 1, solid
unicolor images of four colors Y (Yellow), M (Magenta), C (Cyan), K
(Black) were formed. Unless otherwise specified, each of image
forming conditions is common to the four colors Y, M, C, K.
By setting as A1=A2=2 (mm) for each of image forming areas of
colors Y, M, C, K on the photoreceptor drum, each of the solid
unicolor images was formed all over the image forming area.
Accordingly, the length of the extended toner image becomes 2 (mm)
in both main-scanning and sub-scanning directions.
A recording paper having a thickness of 0.2 (mm) was employed as
the recording medium P.
By employing five kinds of secondary transferring rollers having
the same radius of 15 (mm) and being different from each other in
Asker C hardness of the elastic layer as shown in Table 1, the
image forming operation was conducted with respect to each of them.
The values of B1 and B2 (each equivalent to B) were in a range of
2.4-3 (mm) for everyone of the five kinds of secondary transferring
rollers (2.4 mm<B1, B2<3 mm). In addition, there has been
recognized a tendency that the harder the hardness of the roller
becomes, the greater the values of B1 and B2 increase.
Further, the secondary transferring current at the time of the
secondary transferring operation was set at a predetermined value
and kept constant.
The voltage having a polarity same as that of toner was applied to
the secondary transferring roller between the recording papers, and
the bias cleaning operation was conducted.
The visual inspection was conducted for observing the contamination
of the secondary transferring roller after the secondary
transferring operation was completed, and then, the degree of the
contamination was evaluated as follow.
Excellent: no contamination occurred
Good: practically no problem
Passable: recognizable level
Bad: fully visible contamination band occurred
Example 2
The image forming operation and the evaluation were conducted under
the conditions same as those of EXAMPLE 1, except that A=A1=A2=2.4
(mm) was set.
Example 3
The image forming operation and the evaluation were conducted under
the conditions same as those of EXAMPLE 1, except that the
transferring bias waveform as shown in FIG. 7 was employed, and the
transferring bias was lowered for the extended toner image
developed in the image forming area A1 extended downstream in the
conveyance direction of the recording medium.
Example 4
The image forming operation and the evaluation were conducted under
the conditions same as those of EXAMPLE 1, except that the
transferring bias waveform as shown in FIG. 7 was employed, and the
transferring bias was lowered for the extended toner image
developed in the image forming area A1 extended downstream in the
conveyance direction of the recording medium.
Example 5
The image forming operation and the evaluation were conducted under
the conditions same as those of EXAMPLE 1, except that the
developing operation was conducted by substituting toner of colors
Y, M, C for the black toner without employing the black toner all
over the image forming area as shown in FIG. 8(b).
Example 6
The image forming operation and the evaluation were conducted under
the conditions same as those of EXAMPLE 2, except that the
developing operation was conducted by substituting toner of colors
Y, M, C for the black toner without employing the black toner all
over the image forming area as shown in FIG. 8(b).
Comparison Example 1
The image forming operation and the evaluation were conducted under
the conditions same as those of EXAMPLE 1, except that A=A1=A2=3
(mm) was set.
The evaluation results of examples 1-6 and comparison example 1 are
shown in Table 1.
TABLE-US-00001 TABLE 1 Length of extended Roller hardness (Asker C
hardness) image A 25.degree. 30.degree. 50.degree. 70.degree.
75.degree. Example 1 2 mm Good Excelent Excelent Excelent Excelent
Example 2 2.4 mm Passable Good Excelent Excelent Excelent Example 3
2 mm Excelent Excelent Excelent Excelent Excelent Example 4 2.4 mm
Good Excelent Excelent Excelent Excelent Example 5 2 mm Excelent
Excelent Excelent Excelent Excelent Example 6 2.4 mm Excelent
Excelent Excelent Excelent Excelent Comparison example 1 3 mm Bad
Bad Bad Bad Bad
Compared to comparison example 1, the degrees of contamination in
examples 1-6 were low. Accordingly, the effect of preventing the
contamination, to be attained in the present invention, was
confirmed.
Further, with respect to each of examples 1-6, it was confirmed
that the effect for preventing the contamination of the secondary
transferring roller could be improved by setting the hardness of
the elastic layer at a value equal to or greater than 30.degree..
However, when setting it at 75.degree., a certain level of
instability was recognized in the transferring operation.
Still further, with respect to examples 3 and 4, it was confirmed
that the contamination of the secondary transferring roller could
be reduced to further lower level, compared to examples 1 and 2,
and the effect for preventing the contamination of the secondary
transferring roller could be improved, by setting the transferring
bias to be applied to the extended toner image developed on the
image forming area A1, extended downstream in the conveyance
direction of the recording medium P, at a low value. With respect
to examples 5 and 6, it was also confirmed that the contamination
of the secondary transferring roller could be reduced to further
lower level, compared to examples 1 and 2, and the effect for
preventing the contamination of the secondary transferring roller
could be improved, by excluding the toner of color K (black toner)
in the developing operation for all over the image forming
area.
While the preferred embodiments of the present invention have been
described using specific term, such description is for illustrative
purpose only, and it is to be understood that changes and
variations may be made without departing from the spirit and scope
of the appended claims.
* * * * *